1. Field of the Invention
The present invention relates to an ink-jet type recording apparatus applied to, for example, a printer or a facsimile, and to a technique for preventing ink in a nozzle opening portion from thickening and drying with intent to stably eject an ink drop.
2. Description of the Related Art
Up to now, an ink-jet type recording apparatus has been known which records characters, images, etc. on a recording medium by using an ink-jet head having a plurality of nozzles for ejecting ink. In such an ink-jet type recording apparatus, the ink-jet head is provided in a head holder such that the nozzles of the ink-jet head are opposed to the recording medium, and the head holder is mounted on a carriage, and scanning is performed in a direction orthogonal to the direction in which the recording medium is conveyed.
FIG. 8 is a schematic exploded view of an example of a head tip of such an ink-jet head, and FIG. 9 is a sectional view of a main part thereof.
As shown in FIGS. 8 and 9, a plurality of chambers 102 are arranged side by side in a piezoelectric ceramic plate 101, the chambers 102 being separated from each other by side walls 103. One longitudinal end portion of each chamber 102 extends to one end surface of the piezoelectric ceramic plate 101, and the other end portion thereof does not extend to the other end surface. The depth of each chamber 102 gradually decreases along the length thereof. Longitudinally extending electrodes 105 for drive electric field application are formed on openingside surfaces of both side walls 103 of each chamber 102.
Further, a cover plate 107 is joined to the side of the piezoelectric ceramic plate 101 where the chambers 102 are open through the intermediation of an adhesive 109. The cover plate 107 has a common ink chamber 111 constituting a recess communicating with the shallow other end portions of the chambers 102 and an ink supply port 112 extending from the bottom of the common ink chamber 111 to the side opposite to the chambers 102.
Furthermore, a nozzle plate 115 is joined to the end surface of a joint unit of the piezoelectric ceramic plate 101 and the cover plate 107 where the chambers 102 are open, and nozzle openings 117 are formed at positions of the nozzle plate 115 opposed to the chambers 102.
Note that, a wiring substrate 120 is fixedly bonded to the surface of the piezoelectric ceramic plate 101 on the side opposite to the cover plate 107 and on the side opposite to the nozzle plate 115. A wiring 122 is formed on the wiring substrate 120, which is connected by the electrodes 105, bonding wires 121, etc., and a drive voltage can be applied to the electrodes 105 through the wiring 122.
In this head tip constructed as described above, the chambers 102 are filled with ink from the ink supply port 112. When a predetermined drive electric field is caused to act on both side walls 103 of the given chamber 102 through the electrodes 105, the side walls 103 undergo deformation and the volume of the chamber 102 temporarily changes, so that ink in the chamber 102 is ejected from the nozzle opening 117.
For example, when, as shown in FIG. 10, ink is to be ejected through the nozzle opening 117 corresponding to a chamber 102a, positive drive voltage is applied to electrodes 105a and 105b in the chamber 102a, and electrodes 105c and 105d respectively opposed thereto are grounded, by which a drive electric field directed to the chamber 102a is applied to side walls 103a and 103b. When this is orthogonal to the polarization direction of the piezoelectric ceramic plate 101, the side walls 103a and 103b are deformed toward the chamber 102a by the piezoelectric thickness slippage effect, and the volume of the chamber 102a decreases to cause an increase in pressure on the ink, thereby causing ink to be ejected through the nozzle opening 117.
In such an ink-jet head, the ink in the nozzle opening portion in which ejection operation is performed at frequent intervals hardly dries because new ink is successively supplied. However, when the ejection state of the ink is stopped or when non-ejection data is successively inputted to the same chamber, the ink in the nozzle opening portion is left to be exposed to the air, it dries and thickens. If the ink is ejected in this state, an ejection speed is reduced, the ink droplet flies off course, and clogging is caused.
Thus, there has been proposed that the operation for evacuating the thickened ink is performed at regular intervals by moving the head to the outside of a printing region to forcedly eject the ink or by sucking it in a state in which a cap is in contact with the nozzle plate side
In the above-mentioned method of evacuating the thickened ink, the evacuation of the ink causes increased ink consumption and it is necessary to stop printing, so that a printing rate reduces. In order to solve this, there has been proposed a method in which the piezoelectric ceramic is driven to vibrate the meniscus at a voltage low enough to prevent ink ejection so that the thickened ink on the surface of the meniscus is agitated (for example, see Patent Document 1 and Patent Document 2).
[Patent Document 1]
JP 55-123476 A (page 5)
[Patent Document 1]
JP 57-61576 A (pages 1–2, FIG. 2)
However, in the above-mentioned method of vibrating the meniscus at a voltage low enough to keep from ink ejection, when the meniscus is vibrated on a nozzle in which the ink is not ejected in accordance with the specification of the recording data during printing operation, it is necessary to change a voltage applied to a nozzle according to whether or not the ejection is performed. Therefore, there is a problem in that voltage control and a driver circuit are complicated.